In recent years, rechargeable and dischargeable electric storage devices such as battery cells (e.g., a lithium ion battery cell and a nickel-metal hydride battery cell) and capacitors (e.g., an electric double layer capacitor) have been adopted as the power sources of vehicles (e.g., an automobile and a motorcycle) and various devices (e.g., a portable terminal and a laptop computer). For example, a battery cell includes an electrode assembly and a case composed of a case body which houses the electrode assembly and a cover plate which covers an opening of the case body. An external terminal is arranged at an outer surface of the cover plate, a current collector is connected to the electrode assembly, the current collector is arranged inside the case, and the external terminal and the current collector are directly or indirectly connected to each other. With this configuration, the external terminal and the electrode assembly are electrically connected.
There are two main methods for connecting an external terminal and a current collector. One is to directly connect an external terminal and a current collector, and the other is to indirectly connect an external terminal and a current collector via an auxiliary terminal and a connecting conductor.
The former method uses an external terminal which is composed of a body, a crimping part projecting from a lower surface of the body (and as necessary, a male thread part projecting from an upper surface of the body). The external terminal is arranged at an outer surface of a cover plate via a sealing member, the crimping part of the external terminal is inserted into a through-hole of a current collector inside a case, and an end portion of the crimping part projecting downward from the through-hole is crimped from below. With this configuration, the external terminal and the current collector are directly connected to each other.
The latter method uses an auxiliary terminal composed of a body, a first crimping part projecting from a lower surface of the body, and a second crimping part projecting from an upper surface of the body, an external terminal composed of a head and a male thread part projecting from an upper surface of the head, and a connecting conductor including through-holes into which the second crimping part of the auxiliary terminal and the male thread part of the external terminal are to be inserted. The auxiliary terminal is arranged at an outer surface of a cover plate via a sealing member, the first crimping part of the auxiliary terminal is inserted into a through-hole of a current collector inside a case, and an end portion of the first crimping part projecting downward from the through-hole is crimped from below. The external terminal is arranged at the outer surface of the cover plate via the sealing member or via a terminal retainer provided separately from the sealing member, the second crimping part of the auxiliary terminal and the male thread part of the external terminal are inserted into the through-holes of the connecting conductor, and an end portion of the second crimping part projecting upward from the through-hole is crimped from above. With this configuration, the external terminal and the current collector are indirectly connected via the auxiliary terminal and the connecting conductor.
The battery cell described in Patent Document 1 (JP-A-2006-216410 is fabricated by the former method as mentioned above. An external terminal (electrode guide pin 6) includes a body (head 6B) and a crimping part (columnar part 6A). An insulating sealing member (insulating member 4) includes a surrounding circumferential outer wall part, a recess inside the outer wall, a through-hole in the bottom surface of the recess and an annular projection (tubular part 4B) that projects around the through-hole, the annular projection being inserted through a through-hole (through hole 10) formed in the cover plate (metal plate 3). The body (head 6B) of the external terminal (electrode guide pin 6) is inserted through a recess of the insulating sealing member (insulating member 4). The crimping part (column part 6A) is inserted through a through-hole of a connection part (conductive tab connection plate 11) of a current collector via the through-hole in the bottom surface of the recess. An end portion of the crimping part, which projects downward from the through-hole of the connection part (conductive tab connection plate 11), is crimped from below. In this manner, the external terminal (electrode guide pin 6) is attached to the cover plate (metal plate 3) while being electrically connected to the connection part (conductive tab connection plate 11) of the current collector and insulated from the cover plate (metal plate 3).
However, in the battery cell described in Patent Document 1, the cover plate (metal plate 3) is made of a soft material such as an aluminum-based metallic material. Because of this, when the external terminal (electrode guide pin 6) is crimped, the surface of the cover plate (metal plate 3) is subjected to compression stress and deformed due to pressing force from the insulating sealing member (insulating member 4), which leads to a decrease in flatness. This results in reducing the degree of contact between the surface of the cover plate (metal plate 3) and the surface of the insulating sealing member (insulating member 4), and therefore impairing sealing performance in this region. Furthermore, if the insulating sealing member (insulating member 4) is harder than the cover plate (metal plate 3), creep occurs in the insulating sealing member (insulating member 4), which also results in reducing the degree of contact between the surface of the cover plate (metal plate 3) and the surface of the insulating sealing member (insulating member 4), and therefore impairing sealing performance in this region.
This problem occurs not only in battery cells but also in capacitors (e.g., a double layer capacitor and the like) as well.